1. Technical Field
The present disclosure relates to a light emitting diode (LED) backlight unit, and more particularly, to a backlight unit that can uniformly emit light from LEDs to a light guide plate and a liquid crystal display having the backlight unit.
2. Description of the Related Art
A liquid crystal display (LCD) device is a flat display device for displaying an image, and has been widely utilized as a monitor for a computer, a television set or the like, because of its advantage of thin profile, light weight and low power consumption. The LCD device typically includes a liquid crystal panel for displaying an image and a backlight assembly for emitting light to the liquid crystal panel.
The backlight assembly may be classified into an edge-type and a direct-type according to the disposition of a light source. The edge-type backlight assembly includes a light guiding plate and a light source disposed on a side surface of the light guiding plate. The light guiding plate serves to guide light emitted from the light source frontward. The direct-type backlight assembly is suitable for a large-sized (e.g., more than 12-inch) LCD device, and includes a plurality of light sources formed on a rear surface of the liquid crystal panel. The light emitted from the light sources is directly emitted to the liquid crystal panel.
The light source of the backlight assembly may be selected from any one of an electro luminescence (EL), a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), and a light emitting diode (LED). The LEDs include red, green and blue LEDs and also white LEDs. Since the LEDs have the advantage of maintaining the uniformity of the light while reducing a thickness of the LCD device, the LEDs can contribute to a high luminance backlight assembly.
FIG. 1 is an exploded perspective view illustrating an edge-type LCD device having LEDs, and FIG. 2 is a top view illustrating luminance of the LCD device of FIG. 1 according to the related art. As shown in FIGS. 1 and 2, the related art edge-type LCD device includes a liquid crystal panel 10, and a backlight assembly 20 that emits light to the liquid crystal panel 10.
Referring to FIG. 1, the backlight assembly 20 includes a bottom cover 90, a reflective plate 70, a light guiding plate 50, a plurality of optical sheets 30, and a plurality of LEDs 60. The LEDs 60 are disposed at a side of the bottom cover 90 and spaced apart from each other. The backlight assembly 20 further includes a printed circuit board (PCB) 61 provided with an electric conductive pattern to supply electric power to the LEDs 60, and a housing 62 enclosing the LEDs 60 to guide the light generated from the LEDs 60 to the light guiding plate 50.
Referring to FIG. 2, the LEDs 60 and the light guiding plate 50 are disposed on an identical plane such that the light generated from the LEDs 60 is incident on a side surface of the light guiding plate 50. Moreover, the LEDs 60 have an emission angle of about 100°, and thus the light emitted from the LEDs 60 is incident on the incident surface of the light guiding plate 50. Due to the medium difference at the incident surface of the light guiding plate 50, the light path is changed.
However, in the related art LCD, the emission angle of the light emitted from the LEDs 60 and incident on the incident surface of the light guiding plate is reduced by the medium difference. As a result, bright portions A and dark portions B are alternately generated at the incident surface area of the light guiding plate 50, causing hot spots where the luminance is not uniform at areas where the LEDs 60 are disposed.